It depends on what you like. I would do Star Tours, Space Mountain and grizzly River Rapids or Screamin' (or if you don't have time to cross over to DCA, do ST, SM and Matterhorn.)
California Screamin' is a great roller coaster and I love it, but if you ever go to any other amusement parks like Six Flags, then I would skip it in favor of the other rides on your list. If you have the time, then go for it. An adrenaline rush for sure.
I hate Tower of Terror because I can't take the drops. The freefall is terrifying to me and the rest of the ride (the story behind it) is unimpressive. Lame, actually. Not scary, not interesting. Unless you really love freefall rides, skip this one.
Space Mountain is my all-time favorite roller coaster! It is fast, relatively smooth and a beautiful, in the dark ride with great soundtrack that makes you feel like you're almost in space. But do get a fast pass if you can, or make sure to get in line right before park closing. If you are in line when the park closes, you still get to ride.
Star Tours is amazing and waiting in line is half the fun. Out of all the rides on your list, this is the one I would be willing to stand in line a while for, just because the que area is so entertaining. In fact, I hate to use fastpasses here because you miss out on half the ride by zipping through the que. If you like the Star Wars movies, even a little bit, do not miss this ride. It is a 3D simulated ride and I usually do not like 3D movies but on this ride I forget I even have 3D glasses on. The story and the ride are extremely well done.
Grizzly River Rapids is one of my favorites but I like it better in the daylight hours. And it is more fun to go on this with people in your group because half the fun is screaming and laughing over who in your raft is going to get drenched or go down the next drop backwards. You will get wet and may get absolutely soaked, so go on this one last and if it is not a warm night, you'll have to decide if a cold, wet walk back to your car/shuttle/hotel is worth it. Or you can bring a pair of flip flops, running shorts and an extra t-shirt and change before/after the ride. There are lockers nearby for your things or you can put your backpack in a big plastic bag to keep it dry.
Matterhorn is fun and probably more thrilling at night and I really like it but it has never been one of my must-dos. It is a speedy bobsled ride on tracks through a mountain with a few sightings of a growling snow monster. Not a great roller coaster but still really fun. Disney does such a fine job theming their rides and this one is a good example of that. It was the very first coaster-type ride at DL.
Have fun and please let us know what you end up getting to do!
and Grizzly (too wet).
With Matterhorn, when we took my mom on it, she didn't like it because it was too bumpy and hurt her back, but then we took her through the other side of it, and she liked that one a lot better. I think the bumpier side is the Tomorrowland side (we just call it the left side, so I can never remember which part of the park is where relative to the lines). This one is definitely my all-time favourite ride.
We ended up riding it three times that trip, and we've even shuffled around our September trip so that we can be there when it's open. But Matterhorn is still totally my favourite of the two.
